using Microsoft.Extensions.Options;
using ZB.MOM.WW.Auth.Abstractions.Ldap;

namespace ZB.MOM.WW.Auth.Ldap;

/// <summary>
/// Validates <see cref="LdapOptions"/> at startup so a misconfiguration fails fast at
/// boot with a clear, field-naming message — rather than surfacing later as an opaque
/// low-level error on the first real login attempt.
/// </summary>
/// <remarks>
/// Validation is skipped entirely when <see cref="LdapOptions.Enabled"/> is <c>false</c>
/// (a disabled provider's connection fields are inert). When enabled, four conditions
/// are enforced:
/// <list type="bullet">
/// <item>plaintext transport (<see cref="LdapTransport.None"/>) is rejected unless
/// <see cref="LdapOptions.AllowInsecure"/> is explicitly set (dev/test only);</item>
/// <item><see cref="LdapOptions.Server"/> must be specified (no sane default host);</item>
/// <item><see cref="LdapOptions.SearchBase"/> must be specified (the DN root every
/// search runs against);</item>
/// <item><see cref="LdapOptions.ServiceAccountDn"/> must be specified — an empty value
/// would bind anonymously, defeating the search-then-bind authentication flow.</item>
/// </list>
/// </remarks>
public sealed class LdapOptionsValidator : IValidateOptions<LdapOptions>
{
    /// <inheritdoc />
    public ValidateOptionsResult Validate(string? name, LdapOptions options)
    {
        ArgumentNullException.ThrowIfNull(options);

        // When LDAP is disabled, its connection fields are inert — do not require them.
        // A consumer that turns LDAP off should not have to supply a server/search-base/
        // service-account just to satisfy startup validation.
        if (!options.Enabled)
        {
            return ValidateOptionsResult.Success;
        }

        if (options.Transport == LdapTransport.None && !options.AllowInsecure)
        {
            return ValidateOptionsResult.Fail(
                $"{nameof(LdapOptions.Transport)} is {nameof(LdapTransport.None)} (insecure/plaintext) " +
                $"but {nameof(LdapOptions.AllowInsecure)} is false. Enable TLS " +
                $"({nameof(LdapTransport.Ldaps)} or {nameof(LdapTransport.StartTls)}) " +
                $"or set {nameof(LdapOptions.AllowInsecure)} for dev/test.");
        }

        if (string.IsNullOrWhiteSpace(options.Server))
        {
            return ValidateOptionsResult.Fail(
                $"{nameof(LdapOptions.Server)} is required but was empty or whitespace — " +
                "set it to the LDAP server hostname or IP (e.g. \"ldap.example.com\").");
        }

        if (string.IsNullOrWhiteSpace(options.SearchBase))
        {
            return ValidateOptionsResult.Fail(
                $"{nameof(LdapOptions.SearchBase)} is required but was empty or whitespace — " +
                "set it to the search-base DN (e.g. \"dc=example,dc=com\").");
        }

        if (string.IsNullOrWhiteSpace(options.ServiceAccountDn))
        {
            return ValidateOptionsResult.Fail(
                $"{nameof(LdapOptions.ServiceAccountDn)} is required but was empty or whitespace — " +
                "an empty value would bind anonymously. Set it to the service-account DN " +
                "(e.g. \"cn=svc,dc=example,dc=com\").");
        }

        return ValidateOptionsResult.Success;
    }
}
